While the availability of vaccines efficiently protects individuals from infection with influenza virus, there is still a great need for specific antiviral drugs that prevent disease progression and virus transmission. This will be particularly important during either an epidemic or pandemic outbreak where prior vaccination is unlikely to confer protection, therefore increasing the susceptible population. It is also advantageous to have at least two antiviral drugs (aimed at different targets) available due to the rapid emergence of resistant virus strains. Of the two current classes of FDA-approved influenza virus antiviral drugs, only the neuraminidase inhibitors remain effective against current circulating viruses, so the time has come to develop new and improved antiviral drugs against influenza virus. Unlike our predecessors, we have the advantage of working in the post-genomic era and this affords us the ability to expand the number of potential drug targets to include those host proteins that the virus needs to complete its replication cycle. Our first aim in this proposal is to identify these cellular requirements through the use of RNA interference technology. In addition to identifying requirements of essential replication pathways, we will also strive to find host factors involved in virus pathogenesis, which ultimately determines disease severity. For this purpose we will focus on the anti-interferon properties of the influenza NS1 protein which is a proven determinant of virulence. In specific aim 2 we will select the lead host factors for use as targets in biochemical assays to detect small molecules with specific inhibitory activity against these proteins. We hypothesize that these compounds will also have anti-influenza virus activity and in fact may have an advantage over drugs that target viral proteins, as resistance is less likely to develop. To further identify candidate antiviral drugs, we will also conduct a screen to identify small molecule inhibitors of influenza virus growth in a cell-based assay. The challenge of identifying the targets of these compounds will most likely favor the selection of inhibitors of viral proteins but with the benefit that their efficacy in vivo is part of the selection criteria. Therefore, using two distinct approaches we aim to identify influenza virus specific antiviral compounds that target both viral and host requirements for influenza virus growth and to initiate pre-clinical evaluation of the lead compounds.